A step transformer has a rotor that is moved angularly in steps to switch the transformer output and/or input to different taps on the transformer. A terminal must be moved from one tap to the next one with the highest possible starting speed to avoid drawing an arc or to break any arc drawn as quickly as possible. It is therefore common to provide a spring-loaded force-storing actuator for such a load switch. Movement of an input element in a direction intended to switch the rotor of the transformer is first merely transferred to this force-storing device to compress and/or extend the spring or springs thereof. Once a critical point is reached, this stored-up spring force is released to snap the rotor angularly to the next position. This therefore allows a relatively slowly moving motor to drive the rotor of the step transformer with the desired snap action.
In copending patent application Ser. No. 07/613,387 I describe such an arrangement for connection to a rotor of a step transformer that has a pair of similar levers rotatable about a common axis and having diametrally opposite outer ends, an input element and an output element rotatable about the axis and operatively engageable with the levers, and a latch device for releasably retaining the output element in any of a plurality of angularly offset positions. Respective springs each have one end connected to a respective end of one of the levers and an opposite end connected to a respective end of the other lever and having a middle between the ends. Respective guides movable freely angularly about the axis between the lever ends at generally the same radial spacing from the axis as the lever ends are connected to the middles of the respective springs. Thus the springs each have a pair of sections flanking the respective guide and extending generally tangentially of a circle centered on the axis from the respective spring ends to the respective spring middles.
Thus the springs are in effect deflected so that they are effective almost purely angularly on the ends of the levers. As a result the mechanism is extremely simple while still giving the desired snap action needed to avoid arc formation in a step transformer.
The main disadvantage of this system is that it is fairly complex and bulky. The complexity makes it difficult and expensive to manufacture. The bulkiness makes accommodating it in the bottom of a standard step transformer fairly difficult.